This invention relates to wireless common carrier telecommunications systems, such as cellular telephone systems and, more particularly, to the generation in such systems of tones of the type normally sensed by a user of a conventional land-line telephone. The present invention also is applicable to land-line telephone systems of the type having a switch that operates with "out-of-band" signalling.
A typical wireless common carrier telecommunications system, such as a cellular telephone system, a personal communications system, or the like, provides communication between a base station located in a particular cell and a cellular telephone (or a personal communication device) which may be mobile and may move from one cell to another. The user of the cellular telephone (for convenience, as used herein, "cellular telephone" is intended to refer to both cellular telephones and personal communication devices, as well as other analogous communication equipment) normally subscribes to a particular service provider which provides telecommunications service in a number of cells throughout a particular geographical area. The service provider to which the user of the cellular telephone subscribes is referred to as the HOME system and, typically, favorable features are available from and beneficial tariffs are charged by the HOME system.
When the user of the cellular telephone is located in a cell that is serviced by a service provider to which the user does not subscribe, the user is referred to as a ROAMER, and is subject to higher tariffs for telecommunications service. To reduce the likelihood that a user may ROAM into a cell that is serviced by a service provider to which he does not subscribe, a heavy user of cellular telephone service may subscribe to a secondary service provider, referred to as an alternate HOME system. Of course, there is the possibility that the user may find himself in a geographical area in which no cellular telephone system is available.
In the foregoing instances, when power is supplied to the cellular telephone, as by actuating a POWER switch, thereby initiating an initialization operation, the service indication of the type of service that is available to the user (i.e. HOME, alternate HOME, ROAM or NO SERVICE) typically is provided by a visual indication on the cellular telephone device itself. This is derived from the usual Overhead Message Train transmitted from a base station via a Forward Control Channel and received by the cellular telephone device which detects the overhead message train and provides the appropriate indication derived therefrom. This, of course, is a method of using a telephone which is quite different from that with which a typical telephone user has become accustomed. That is, the usual audible tones which normally are present in a land-line telephone system, such as dial tone, service availability, busy circuits, and the like, are not present in cellular telephone systems.
The foregoing feature of providing an Overhead Message Train in a Forward Control Channel which is separate from the channel in which audio communication is transmitted (voice signals communicated from the base station to the cellular telephone are transmitted over a forward audio channel and voice signals communicated from the cellular telephone back to the base station are transmitted over a reverse audio channel) is referred to as out-of-band signalling (the communication of voice signals between the cellular telephone and the base station is referred to as in-band signalling). Such out-of-band signalling is not limited solely to cellular telephone systems, and often is found in land-line telephone switches having serving nodes which indicate service availability and respond to "line request" messages with "line granting" responses, analogous to the messages transmitted over the forward and reverse control channels in a cellular telephone system. Here too, out-of-band signalling in a land-line system furnishes a user with indications with which he may not be accustomed. That is, the various dial tones normally generated in conventional telephone systems may not be present in a land-line system which uses a switch providing out-of-band signalling.
It also is a characteristic operational feature of cellular telephone systems (and other out-of-band signalling systems) to assemble telephone number data and then transmit that data to the base station to initiate a "dialing" operation. Typically, the keys of the cellular telephone keypad are actuated and the actuation of each key is displayed. When the user observes the display of a complete telephone number, the usual SEND key is operated, thereby transmitting to the base station over the reverse control channel the assembled telephone number data. There is, however, no preliminary analysis of the assembled telephone number data prior to its transmission to the base station. As a result, errors that may be made by the user, such as entering an erroneous area code, entering too few or too great a number of digits, or the like, are not uncovered until the telephone number data is analyzed at the base station. Consequently, unnecessary delays may be introduced into completing a correct telephone call or indicating an erroneous telephone number, thereby providing a level of frustration to the user of the telephone equipment.
It is recognized, then, that the operation of a cellular telephone or other out-of-band telephone system differs from the operation of a conventional land-line telephone. The absence of dial tones and DTMF tones when generating telephone number data can be troublesome to the novice user of cellular telephone equipment. Also, the various visual indications associated with cellular telephones is implemented by costly and power consuming devices which adds to the price of consumer equipment.